This Application is a 371 of PCT/IT98/00266, filed on Oct. 6, 1998.
The present invention concerns the use of flunarizine for the topical treatment of glaucoma. More specifically, this invention relates to the use of flunarizine, a calcium channel blocking agent known and employed as cerebral and peripheral vasodilator, in a new indication as an antiglaucoma agent for topical ophthalmic treatment.
As it is known, glaucoma is a pathological ophthalmic condition the underlying causes of which are not well understood at present. This condition is usually shown by a progressive increase of the intraocular pressure, leading to severe impairment of the eye structures, in particular to damage to the optic nerve disc and to decrease in the visual field, finally resulting in optic atrophy. The disease is generally connected to an insufficient outflow of aqueous humour from the eye, although other causes, such as, e.g., the production of aqueous humour and the episcleral veins pressure, take part in the regulation of the intraocular pressure.
The rationale of the pharmacological therapy presently in use is to lower the intraocular pressure. The drugs currently used to that aim, divided into classes according to their mechanism of action, are beta-blockers (such as timolol, betaxolol, levobunolol), sympathomimetics (such as epinephrine and dipivephrine), parasympathomimetics or miotics (such as pilocarpine and acetylcholine) and carbonic anhydrase inhibitors (such as acetazolamide and dichlorphenamide). Besides the foregoing drugs well established in use, the search for agents having less side effects and longer lasting activity has lead to evaluate, more recently, the possibility of using for the treatment of glaucoma another class of drugs, i.e. the calcium blocking agents. The latter, also known as xe2x80x9ccalcium entry blockersxe2x80x9d or xe2x80x9ccalcium antagonistsxe2x80x9d, are currently used as vasodilators and in the treatment of cardiac affections. For such indications, the most widespread calcium antagonists are, e.g., nifedipine, diltiazem and verapamil.
The role of calcium in the dynamics of aqueous humour and in the control of intraocular pressure has not yet been entirely clarified, although it is known that the production and the outflow of aqueous are modulated also by calcium. As concerns the formation of aqueous, it is to be noted, firstly, that the hydrostatic component due to the arterial pressure and to the pressure of the vessels feeding the ciliary body is calcium-dependent, as it is confirmed by the known systemic vascular action of calcium antagonists. Further, the osmotic pressure due to ionic secretion at the level of the non-pigmented ciliary epithelium is likely to be modulated by calcium, as hypothesised by Abelson et al. (Abelson M. B., Gilbert C. M., Smith L. M., Sustained reduction of intraocular pressure in humans with the calcium channel blocker verapamil, Am. J. Ophthamol. 105; 155 (1988)).
As far as the outflow of the aqueous humour is concerned, calcium ions play a direct role in modulating the pressure of episcleral veins, and some studies suggest that calcium influences the outflow capacity, by maintaining the structural integrity of the trabecuale and of the exterior wall of the Schlemm""s canal.
In spite of the foregoing suggestions several experimental works, both on animal models and clinical, and involving both systemic and topical administration, reported contradictory results about the activity of calcium channel blockers in the therapy of glaucoma. For instance, Monica et al. (Monica M. L., Hesse R. J., Messerli F. H., The effect of a calcium-channel blocking agent on intraocular pressure, Am. J. Ophthalmol. 96, 814 (1983)) reports that the oral administration of nitrendipine to patients with moderate hypertension but with normal intraocular pressure slightly lowered the latter, while Beatty and co-workers (Beatty J. F., Krupin T., Nichols P. F., Elevation of intraocular pressure by calcium-channel blockers, Arch. Ophthalmol. 102; 1072, (1984)) did not evidence any effect upon oral administration of verapamil to rabbits, and did even report an increase in the intraocular pressure upon topical administration. More recently, for instance, Payene and coworkers (Payene, L. J., Slagle T. M., Cheeks L. T., Effect of calcium-channel blockers on intraocular pressure, Ophthalmic Res. 22; 337, (1990)) obtained a reduction in the intraocular pressure upon systemic administration of verapamil or nifedipine to rabbits, but did not detect any significant effect upon topical administration of the same agents or of diltiazem by the topical route.
In general, however, at least as far as verapamil is concerned, it may be said that the administration of this drug to man normally results in a reduction of the intraocular pressure. A more consistent reduction upon topical administration has been explained, in particular, by a work of Ettl et al. (Ettl A., Daxer A., Hoffmann U., Calcium channel blockers in the management of low-tension and open-angle glaucoma, Am. J. Ophthalmol. 116; 778, (1993)). These authors have detected, in the rabbit eye, verapamil levels 200 times higher than the levels obtainable by systemic administration.
Accordingly, the use of verapamil in the treatment of ocular hypertension is the object of the international PCT application No. WO 92/07563, filed by Abelson (i.e., the first author cited above) et al. A later publication in the name of the same author is the international application No. WO 96/03986, concerning the treatment of a particular form of glaucoma, referred to as low-tension glaucoma. This pathology is characterised by an intraocular pressure which is almost normal, in spite of the fact that all of the other symptoms of glaucoma are present. In the latter document the therapeutic proposal is generically extended to all calcium-antagonists, many representatives of which are mentioned in a preliminary list. However, the only example of active agent disclosed in the document and supported by experimental data is verapamil.
Another calcium blocking agent that was specifically proposed for use, in a patent document, in the treatment of intraocular hypertension is diltiazem (French patent No. 2593395, published in 1987), while a list of more than one hundred calcium antagonists is presented in the international PCT application No. WO 93/23082. The latter concerns, for use in the treatment of glaucoma, a combination of a compound which lowers the intraocular pressure (i.e., a conventional antiglaucoma agent) and a calcium channel blocking agent. The disclosure does not contain any specific example of preferred combination, nor any experimental detail regarding the activity of any combination.
Some experimental trials on verapamil also allowed to ascertain that the ophthalmic use of the said agent causes an undesirable swelling of the cornea. (Green K., Cheeks L., Hull D. S., Effects of calcium channel blockers on rabbit corneal endothelial function, Curr. Eye Res. 13; 401-408, (1994)). This is particularly critical if one considers the use for the treatment of a chronic condition as is, actually, glaucoma.
Although the entire class of calcium antagonists has already been considered for its potential use in the treatment of glaucoma, there does not seem to have been evidenced the particular activity, against this type of pathologies, of a specific agent belonging to the said class, i.e. flunarizine. It has now been found, and it is the subject-matter of this invention, that the specific calcium antagonist flunarizine, when administered through the topical ocular route, is able to lower the intraocular pressure in a surprisingly more marked way than the other calcium antagonists so far proposed and tested for the therapy of glaucoma.
Within the frame of the studies connected with this invention, it has also been found that some known receptors, referred to as a receptors, are localised in the ocular region, in particular in the ciliary body and in the iris, and that some specific xe2x80x9cligandsxe2x80x9d, having a "sgr"-agonist activity, significantly lower the ocular pressure. Since it has been experimentally found that flunarizine shows a "sgr"-agonist activity which is far higher than the activity of other calcium antagonists, this property may explain the unexpectedly greater activity of flunarizine in lowering the intraocular pressure, if it is hypothesised that such activity is exerted according to mechanisms of action that are at least partially different from the other calcium blocking agents.
In order to identify the presence of a receptor sites in the eye the technique of xe2x80x9creceptor bindingxe2x80x9d has been exploited. The latter has been carried out on cell membranes obtained from the irido-ciliary body complex. The irido-ciliary body complex had been explanted, after sacrifice, from male albino rabbits of the New Zealand strain. The tissue was homogenised in buffer and a fraction rich in cell membrane proteins was isolated, obtained by centrifugation. The concentration of total proteins has been evaluated by the method of Lowry (Lowry, J. Biol. Chem. 193; 265 (1951)). Aliquots of the said fraction of the homogenate containing 300 xcexcg of total proteins were incubated with scalar amounts of [3H](+)-pentazocine (which is used, for experimental purposes only, as a a ligand). The reaction was carried out at 37xc2x0 C. for 150 minutes and then, after filtering, the radioactivity left on the filters was measured by liquid scintillation. The apparent dissociation constant (Kd) and the total number of receptors were determined, and it was thus ascertained that [3H])(+)-pentazocine selectively binds to receptor sites present in the iridociliary body region of the rabbit. On the basis of the present scientific knowledge, the said receptors appear to be of the type "sgr"-1.
Further, xe2x80x9ccompetitive bindingxe2x80x9d assays carried out with a constant is amount of [3H](+)-pentazocine and scalar amounts of (+)-N-allil-nor-meth-azocine (NANM) (which is used, for experimental purposes only, as a "sgr" ligand), showed that the latter shift the radioactive ligands from the receptor sites. It has also been observed, by analysing the Hill coefficient, that NANM interacts with one only class of a receptor sites.
In the frame of the same research it has been found that "sgr"-agonist agents show an ocular anti-hypertensive activity. A 1% preparation of NANM was administered (50 xcexcl) in the conjunctival fornix of the right eye of male albino rabbits of the New Zealand strain, after measuring the (baseline) intraocular pressure. Upon measuring again the intraocular pressure 60, 120, 180 e 240 minutes after the instillation, it has been ascertained that the intraocular pressure was significantly reduced (p less than 0.01) 60 minutes after the instillation, in comparison with the formulation containing the vehicle only.
Lastly, as it was pointed out before, studies of receptor binding carried out with flunarizine (some of which are presented in the following) have shown that flunarizine has an affinity for "sgr"-1 receptors which is not even comparable to the affinity shown by the other calcium channel blocking agents tested.
Another advantageous aspect distinguishing flunarizine from the other calcium channel blocking agents proposed so far for the topical treatment of glaucoma is, as it has now been found, that flunarizine does not show any side effect of corneal swelling.
Therefore, the present invention specifically provides the use of flunarizine, optionally in the form of a pharmaceutically acceptable salt, for the topical treatment of glaucoma, i.e. the use of flunarizine, or of a pharmaceutically acceptable salt thereof, in the manufacture of a topical ophthalmic medicament for the treatment and/or the prophylaxis of glaucoma. In general, the topical administration of flunarizine may take place by using a preparation in the form of an aqueous solution or suspension, or in the form a gel, an ointment or a cream in a pharmaceutically acceptable ophthalmic vehicle, or in the form of an erodible ocular insert or of a xe2x80x9creservoirxe2x80x9d system with a polymer membrane, to be placed in the conjunctival sac.
The concentration of flunarizine in an ophthalmic vehicle may range from 10 xcexcg/ml to 5 mg/ml, i.e. from 0.001 to 0.500% by weight. The optimal concentration is chosen firstly on the basis of the dosage to be administered: in the case of use in eye-drop form, for instance, one drop should contain a sufficient amount of flunarizine for the drop to be effective as such or when instilled twice (i.e., two drops). Other criteria for the choice of the concentration are the ocular tolerability (it should be considered that the conjunctival sac, into which the ophthalmic preparation is to be instilled, has a limited capacity) and the stability of the active ingredient. The preferred concentration for an aqueous solution formulation (eye-drops) is 0.050% by weight, and preferably the product is present in the form of the corresponding hydrochloride salt (optimal concentration of flunarizine hydrochloride: 0.052%).
According to a particularly preferred embodiment of this invention, the anti-glaucoma activity of the proposed ophthalmic preparation is further enhanced by the presence, in combination with flunarizine, of an effective amount of a beta-blocking agent. The class of beta-blockers (or xcex2-adrenergic blockers), referred to in the foregoing, represents to date the most widespread class of anti-glaucoma agents. These agents are used in the topical treatment of chronic open angle glaucoma and, more generally, in the treatment of intraocular hypertension. Their mechanism of action mainly consists in reducing the production of the aqueous humour, and therefore the unexpected enhanced activity of the proposed combination of flunarizine (which has been found to be active in increasing the outflow of aqueous) with a beta-blocker may reasonably be explained in terms of a complementarity of the two actions.
Preferably, the concentration of beta-blocking agent in the combination according to the invention is from 0.1 to 2.5% by weight, and most preferably said beta-blocking agent is timolol or a pharmaceutically acceptable salt thereof,
A vehicle that may be employed in an eye-drop preparation according to the invention is the simple physiological saline solution containing 0.9% by weight of sodium chloride. Such solution is isotonic with respect to the tear fluid, and therefore it is well tolerated by the eye. However, also hypotonic solutions or suspensions may be employed, as it is known that these preparations are well tolerated by the ocular tissues.
Other excipients may be added to the composition of the invention in order to adjust the tonicity of the solutions or suspensions, so as to stabilise the active ingredient(s) and to increase the tolerability of the preparation. Specifically, any buffers should maintain the pH into the range 4-8. For instance, the above saline solution may be buffered with any one of the buffers well known in the pharmaceutical art for ophthalmic use, such as, e.g., phosphate buffer, or trizma buffer (i.e., tri-hydroxymethyl amino methane), so as to obtain a physiological pH, in the range of 7.0-7.4. Further, the solution may also have an osmolarity in the physiological range (295-305 mOsm/l). This allows to obtain a better ocular tolerability, In addition, the formulation may advantageously contain an antioxidant, such as, e.g., gallates, ascorbic acid, superoxide dismutase (SOD), BHT, sodium metabisulphite, tocopherols, BHA, nordihydroguaiaretic acid, ascorbic acid esters, dimethylthiourea and the like.
The tolerability may be further enhanced by means of other excipients such as cyclodextrins, polysorbate 80 (or Tween 80), dextrane (e.g., dextrane 70), polyethylene glycol (e.g. PEG 400), poloxamers and other similar agents. The formulation may include viscosifying/thickening agents such as methylcellulose, polyvinyl alcohol, glucosamine glucans, polyvinyl pyrrolidone and the like, in order to increase the ocular bioavailability, the stability and the tolerability of the active ingredient(s).
The ocular bioavailability of flunarizine may be further enhanced by the addition of substances which increase the corneal permeation of the drug, such as, e.g., dimethyl sulphoxide, taurocholates, membrane phospholipides, benzalkonium chloride and other surface active agents for ophthalmic use (such as disodium lauryl sulphosuccinate).
Lastly, in the preparations to be packaged in multidose bottles compositions a preservative with antimicrobial activity will have to be added, in order to prevent contamination of the product. Such agent may be chosen among the preservative agents well known for this use in the pharmaceutical art.
Products to be administered in the form of suspensions should contain suitable agents such as carboxymethyl cellulose and the like. In the event that the preparation is to be employed in the form of an ointment, a gel or a cream for ophthalmic use, flunarizine will be admixed with carriers such as polyethylene glycols, polyacrylates, polyethylene oxides, fatty acids and alcohols or lanolin, paraffin and other similar products. Suitable ingredients for the production of emulsions or microemulsions may be chosen among the following: diethylene glycol-monobutyl ether, di(ethylene glycol) buthyl ether, caprylic acid ethyl ester, oleic acid ethyl ester, soybean oil, hexadecane, tributyrin, ethylene glycol-monobutyl ether, 1-hexadecene, n-heptane, 1-heptene, Tween 80, PEG, poloxamers, polyoxyethylene ethers.
The dosage of the main active ingredient of the invention, to be administered by the topical route, may vary from about 20 xcexcg to about 200 xcexcg per day for each eye. The prescription dosage of the ophthalmic preparations based on flunarizine will depend on the daily dose that will be necessary to achieve the therapeutic effect and, obviously, on the specific formulation employed. Ophthalmic solutions or suspensions will require from 1 to 4 instiliations per day; ointments, gels and creams will require 1 or 2 applications; solid inserts with polymeric matrix, either biodegradable or not, will require one only administration per day.
The present invention further concerns compositions which allow the administration of flunarizine through the topical ophthalmic route, and specific ophthalmic compositions for use in the treatment and/or in the prophylaxis of glaucoma comprising, as an active ingredient, a therapeutically effective amount of flunarizine. A group of preferred compositions have the following formulation (wherein all percentages are by weight):
optionally comprising further pharmaceutically acceptable ingredients.
In a particularly preferred embodiment of this invention, the compositions for use in the treatment and/or in the prophylaxis of glaucoma further contain from 0.1 to 2.5% by weight of a beta-blocking agent, the latter being by preference timolol or a pharmaceutically acceptable salt thereof, such as timolol maleate.
Some specific embodiments of the invention are described below for merely illustrative purposes, together with the results of the experimental studies carried out on the proposed anti-glaucoma agent, including comparative tests with other calcium-blocking agents.
A composition according to the invention that turned out to be particularly effective (the performance of which was experimentally evaluated as it is partly reported further on) has the following composition (the percentages being given by weight):
The above composition is suitable for being packaged in single dose containers; in the event that a multidose packaging is desired, a preservative (such as, e.g., benzalkonium chloride) will have to be added in order to maintain the sterility of the product for the whole period of use.
A composition suitable for use as an ophthalmic ointment was prepared according to the formulation given below (weight percentages):
As a tonicity adjusting agent, 455 mg of sodium chloride per 100 ml (i.e. 0.455 wt. %) may be used in place of the above amount of sorbitol,
An ophthalmic product similar to that shown in the previous example, but having a coarser size of the drops of the dispersed phase, was obtained excluding the soybean oil from the composition, according to the following formulation (weight percentages):
As an alternative to sorbitol as a tonicity adjusting agent, the composition may include 433 mg of sodium chloride per 100 ml (i.e. 0.433 wt. %).
A particularly preferred composition according to the invention was obtained by adding to the formulation of Example 1 a sufficient amount of imolol maleate to achieve a concentration of 0.5% by weight of timolol in the verall composition (corresponding to about 0.68% by weight of timolol maleate). The concentrations of the other ingredients were the same as specified above for Example 1.
Similarly, also the formulations given in Examples 2 and 3 can be modified with the addition of a proper amount of timolol maleate. Also in this case, it is preferred to obtain a concentration of 0.5% by weight of timolol in the overall composition.